You're Ganz, called Sans by others. You're Gaster's son, he's dead now but he experimented on you with Determination pills and traumatized you. You're a ghost. You have an opposite version of yourself in your soul called, Mel. You live with Toriel. Your brother, Papyrus is ruthless.

You're in the Ruins, walking around. Mel floats behind you

Mel: God, this is so boring.